Process for manufacture of shadow mask frames

ABSTRACT

A PROCESS FOR MAKING SHADOW MASK FRAMES FOR TELEVISION SETS WHEREIN A CLOSED WORKPIECE IS EXPANDED TO FORM A CLUSTER OF TWO SHADOW MASK FRAMES, THE WORKPIECE IS TRIMMED TO SEPARATE AND THE FRAMES AND THE FRAMES ARE STUFFED TO REMOVE THE RESIDUAL STRESSES THEREIN.

June 15, 1971 r R. E. ROPER 3,584,366

PROCESS FOR MANUFACTURE OF SHADOW MASK FRAMES Filed Aug. '7, 1968 3 Sheets-Sheet 1 lNV/ENTOQ PAL/ U E, E0052 June 15, 1971 R. E. ROPER 3,584,366

PROCESS FOR MANUFACTURE OF SHADOW MASK FRAMES Filed Aug. 7, 1968 3 Sheets-Sheet 2 Fig. 5

I 40 L; I

/Nl E/VTO/2 RALPH Ev POPE/2 Fig. 6

W MMM W PROCESS FOR MANUFACTURE OF SHADOW MASK FRAMES Filed Aug. 7, 1968 R. E. ROPER June 15, 1971 3 Sheets-Sheet 5 United States Patent O 3,584,366 PROCESS FOR MANUFACTURE OF SHADOW MASK FRAMES Ralph E. Roper, Indianapolis, Ind., assignor to Wallace Expanding Machines, Inc. Filed Aug. 7, 1968, Ser. No. 750,856 Int. Cl. B23p 17/00 US. Cl. 29-412 Claims ABSTRACT OF THE DISCLOSURE A process for making shadow mask frames for television sets wherein a closed workpiece is expanded to form a cluster of two shadow mask frames, the workpiece is trimmed to separate the frames and the frames are stuffed to remove the residual stresses therein.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a process for manufacture of shadow mask frames for television receivers and the like.

Description of the prior art The shadow mask frame of a television receiver is used to mount the shadow mask of the receiver. The shadow mask must be very accurately positioned in the receiver because it includes a large number of tiny holes each in line with a respective set of three color dots on the screen. Thus the mask enables each beam to excite its respective color dots when the beam converges at the correct angle without exciting the other two color dots. If the shadow mask is not accurately positioned the picture will have the wrong colors and will have varying colors across the screen.

It has been the practice to draw the shadow mask frames from a pan shaped workpiece and to anneal the shadow mask after it has been drawn. Such annealing has been done to relieve any inherent or residual stresses produced by the drawing operation. If such residual stresses are not relieved, the shadow mask frame may subsequently deform when the shadow mask is attached thereto or may deform during use either of which will affect the picture. The cost of manufacture of such a part according to present practice and including the annealing step is approximately $1.80. Consequently, it is desirable that an improved process for manufacture of shadow mask frames be provided.

SUMMARY OF THE INVENTION One embodiment of this invention might include a method of making a shadow mask frame which comprises the steps of forming a closed workpiece into the approximate configuration desired for said shadow mask frame, and exerting sufficient columnar force axially of said frame to cause plastic deformation of said frame, and restraining said frame against buckling while under said force whereby said frame reaches its final configuration through plastic deformation of substantially its entire mass.

One object of this invention is to provide an improved method of making a shadow mask frame.

Another object of this invention is to provide a method of making a shadow mask frame which substantially reduces the cost of manufacture of the shadow mask frame from, for example, $1.80 to $0.80.

Still another object of this invention is to provide a method of making a shadow mask frame which produces a better product.

Related objects and advantages will appear as the description proceeds.

3,584,366 Patented June 15, 1971 BRIEF DESCRIPTION OF THE DRAWINGS The full nature of the invention will be understood from the accompanying drawings and the following description and claims.

FIG. 1 is a perspective view of a workpiece used in the process of the present invention;

FIG. 2 is a vertical section taken through expander apparatus used in the process of the present invention;

FIG. 3 is a vertical section similar to FIG. 2 but showing the apparatus in a different operating position than FIG. 2;

FIG. 4 is a perspective view showing the workpiece after it has been operated upon by the apparatus of FIGS. 2 and 3;

FIG. 5 is a section taken through the workpiece of FIG. 4;

FIG. 6 is a vertical section taken through a punching apparatus for punching out portions of the part of FIGS. 3 and 4 to produce a pair of shadow mask frames;

FIG. 7 is a vertical sectional View of a stufiing apparatus showing it in its initial or starting position;

FIG. 8 is a view similar to FIG. 7 but showing the apparatus in a subsequent operating position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularly to the drawings, there is illustrated in FIG. 1 a closed workpiece 10 which has been welded closed along line 11 and which has been preformed into a generally rectangular configuration. In order to form the workpiece 10 into a cluster of shadow mask frames, the workpiece 10 is placed in the apparatus shown in FIG. 2. The workpiece 10 is shown supported on a base 12 between an outer die assembly 15 and an inner die member 16 affixed to the base 12. The outer die assembly 15 includes three die members 17, 20 and 21 which are suitably fixed together to define an inwardly facing recess 22 extending completely around the mechanism of FIG. 2.

The apparatus of FIG. 2 further includes a punch 25 and supporting members 27 and 28 for the punch to which the punch is fixed. The punch 25 has the same outer configuration as the inner configuration of the die member 21 with a space provided between the members 25 and 21 for the thickness of the workpiece. Suitable means (not shown) is provided for moving the punch 25 axially relative to the member 16 and relative to the outer die structure 15 so as to move the punch from the position shown in FIG. 2 to and from the position shown in FIG. 3. It will be noted that the member 27 engages the top of the member 21 limiting the movement of the punch in the position of FIG. 3.

The forming structure of FIG. 2 further includes a urethane pad 30. When the punch is in the upward position of FIG. 2, the urethane pad 30 has the thick configuration illustrated which does not block or interfere with the movement of the workpiece 10 into the forming apparatus. When the punch is moved downwardly to the position shown in FIG. 3, the urethane pad 30 is squeezed and is caused to expand outwardly and to force the workpiece against the forming surfaces of the members 21, 20 and 17 to form the illustrated configuration of FIG. 3.

Referring now to FIGS. 4 and 5, the finally formed workpiece is illustrated after it has been removed from the forming apparatus of FIGS. 2 and 3. It should be understood that the forming apparatus of FIG. 2 can be replaced by other types of expanders such as for example the expander shown in my prior Pat. 2,955,556. This patent also illustrates one way in which the workpiece can be removed from the apparatus of FIGS. 2 and 3.

In order to trim away the scrap portions of the part illustrated in FIGS. 4 and 5, it is necessary to punch or otherwise trim the area marked 35. It will be noted that the corners of the scrap area 35 are marked 35A while the centers of the sides of the scrap portion 35 are marked 35B. Thus, trimming apparatus might be provided which would simultaneously punch out all of the portions 35B after which punching Operation the part illustrated in FIGS. 4- and 5 will be transferred to still another trimming apparatus which would punch out all of the portions A.

Referring to FIG. 6, a portion of a suitable punching device is illustrated. The structure illustrated in FIG. 6 may be repeated four times at 90 angles to punch out either the four areas 35A or the four areas 35B. The punching device includes a mounting plate having secured thereto slide gibs 41. The slide 42 slides upon the mounting plate 40 and within the illustrated gib 41 and a corresponding gib (not shown) on the opposite side of the apparatus. The slides 42 (one shown) are forced outwardly by downward movement of a driver 45 and may be moved inwardly by upward movement of the driver 45, said slide and driver being connected by a T arrangement 44. In order to balance forces the driver 45 is connected to and drives all four of the slides 42. A punch 47 is fixedly mounted on each slide 42. A pressure pad 46 is slidably mounted upon each respective punch 47. Each respective pressure pad 46 is spring biased by compress springs 50 to an outward position.

Fixedly mounted upon each mounting plate 40 is a die block support 51 which has a die block 52 fixedly mounted thereon. Each die block 52 has an indentation or recess 55 which also extends through the die block support 51 and operates to receive the punch 47 for punching out a portion of the workpiece 10. In order to properly position the workpiece the support 51 has a projection 49 fixed thereto. Of course, the workpiece 10 is shown in the configuration which it assumes after being oper ated on by the apparatus of FIGS. 2 and 3. Two of the devices partially illustrated in FIG. 6 might be provided, one for punching out the corners of the workpiece and the other for punching out the centers of the sides of the workpiece. As suggested above, since four of the punches 47 as illustrated in FIG. 6 are provided at 90 to one another, all of the portions 35B can be punched simultaneously. The same is true of the four portions 35A which can be punched out on the second device or machine. After the workpiece has been suitably punched out to cause the cluster of the two shadow mask frames to be separated into separate shadow mask frames, the shadow mask frames are placed into the apparatus of FIGS. 7 and 8.

Referring now to FIGS. 7 and 8 there is fragmentarily illustrated one side of a stuffing apparatus which includes an upper die and a lower die 61. The lower die 61 is fixedly secured to a base plate 62. When the upper die is in its most downward position as illustrated in FIG. 8, the recess provided between the upper die 60 and lower die 61 is somewhat fatter than the shape of the shadow mask frame 62 and it is also somewhat shorter from the end 65 of the recess 66 to the end 67 of the recess 66. Thus, when the upper die 60 moves downwardly against the part 62, the stuffi'ng ledge 68 defined by end 65 of the recess 66 engages the upper end 70 of the part 62 while the stuffing ledge 69 defined by the lower end 67 of the recess 66 engages the lower end 71 of the part 62. Thus the part has a columnar force acting upon it.

Obviously, the part 62 would buckle since it already has a somewhat L-shaped cross section configuration were it not for the fact that the sides of the two dies 60- and 61 confine or restrain the part 62. As the upper die 60 continues its downward movement toward the lower die 61, the columnar force exerted upon the part 62 is so great as to cause substantially the entire part 62 to plas- 4 tically deform and to assume the configuration of the recess between the two dies.

The die structure of FIGS. 7 and 8 can be mounted upon any suitable press arrangement capable of exerting the forces necessary to plastically deform the metal shadow mask frames. A suitable press structure might be an 800 ton Warco Press mechanical drive with a six-inch stroke manufactured by Warco Press Division of McKay Machine Company of Youngstown, Ohio. The plastic deformation of the shadow mask frame causes the inherent or residual stresses produced by the forming operation of the structure of FIGS. 2 and 3 and the trimming of FIG. 6 to be removed from the part. Not only are inherent stresses removed from the part but the markings produced on the part by the trimming operation of the structure of FIG. 6 are also removed by reason of the plastic deformation of the part.

It has been found that by the use of the present invention the cost of forming a shadow mask frame has been reduced from an approximate cost of $1.80 to a cost of $0.80. It has also been found that the shadow mask frame produced by the present invention is a better product than the prior art shadow mask frame in that imperfections in the surface of the part are removed and the part is better able to maintain its configuration when it is used to mount the shadow mask increasing the useful life of the television set.

The invention claimed is:

1. A method of making a shadow mask frame which comprises the steps of forming a closed annular workpiece into the approximate annular configuration desired for said shadow mask frame, and exerting sufiicient columnar force axially of said frame to cause plastic deformation of said frame, and restraining said frame against buckling while under said force by means of surfaces spaced apart a greater distance than the thickness of said frame whereby said frame reaches its final configuration through plastic deformation of substantially its entire mass and residual stresses are relieved without the necessity of annealing.

2. The method of claim 1 wherein said step of forming the closed workpiece comprises the steps of expanding a closed workpiece to form a cluster of two shadow mask frames, trimming said cluster to separate said frames and to form the approximate configuration desired for said frames.

3. The method of claim 1 wherein said frame is caused to assume a new greater thickness by said exerting of force and said restraining said frame.

4. The method of claim 2 wherein said exerting of force and said restraining said frame causes the frame to be molded and the trim lines produced by said trimming step to be removed.

5. A method of making shadow mask frames which 0 comprises the steps of expanding a closed workpiece to form a cluster of two shadow mask frames, trimming said cluster to separate said frames, and stufling said frames to produce plastic deformation of substantially the entire mass of said frames.

References Cited UNITED STATES PATENTS 2,120,595 6/1938 Ash 72-352X 2,715,377 8/1955 Gary 29---412X 2,952,899 9/1960 Glavan 29l48.4 3,295,347 1/1967 Fuessle et a1. 8354X 3,442,110 5/1969 Walton et a1. 72-356X JOHN F. CAMPBELL, Primary Examiner V. A. D. PALMA, Assistant Examiner US. Cl. X.R. 72352, 356; 83-54 

